Card Range To Study

132 Cards in this Set

Front

Back

What is adequate stimulus

adequate stimulus is the "best" stimulus for a given receptor

What is receptive field?

Presentation to the receptor's receptive field (the region of the receptor sheet that causes a change in the response of a receptor or neuron when stimulated) causes ion conductance changes that produces a generator potential

What is generator potential

generator potential is graded, local, and if sufficient to depolarize the neuron beyond threshold, causes action potentials to be generated.

Name the Coding mechanisms available for representing a stimulus in the nervous system

___columns of cells have overlapping receptive fields and respond to the same submodality of stimulation

Vertical

SII cortex: significance is ____.

unknown

Clinical Features of Lesions in the Dorsal Column System

lose precision in discriminative somesthesis. Extent of the deficit is usually proportional to the amount of tissue damage.

Clinical Features of Lesions in the Dorsal Column System

Increase in two-point threshold
Decrease in vibratory sensitivity.
Decrease in precision of position sense and kinesthesia
Increase in spontaneous pain (possibly due to interaction of this system with the anterolateral system

Concept of Pain

quantifiable sensory event,
2) An affective component, the reaction to pain; together these 2 components occur

respond to mechanical, thermal, chemical energy; anything that causes tissue damage. Indicates that a common mechanism might exist, e.g. the release of a chemical from the damaged tissue that stimulates the receptors

Temperature: 2 types,

cold and warm.

Temperature Mechanism

Mechanism probably involves change in the rate of a chemical reaction in the receptor

Touch and pressure -

same as the other mechanoreceptors (dorsal column types).

Itch -

unknown mechanism

(1st order neurons): ipsilateral projection via the dorsal root to the spinal cord.

Primary afferents

First synapse in the ipsilateral spinal cord

1. Enters substantia gelatinosa
2. May ascend or descend 1 or 2 spinal segments before synapse
3. Synapse is in outer layers of the gray matter of the dorsal horn of the spinal cord.

cell body in dorsal horn.

Second order neuron

Axons cross the midline in the spinal cord to form __________.

contralateral anterolateral tract; often called the spinothalamic tract.

CNS targets are widespread, accounts for high arousal properties of

pain

projects to VPL of thalamus and from there to SI and SII. Fast pain, mostly Ad input.

Spinothalamic portion:

projects to the reticular formation in the brainstem. The reticular formation has widespread connections to cortex and therefore has arousal properties; arousal is important for a pain pathway!

Spinoreticular portion:

projects mainly to a nucleus known as the periaqueductal gray matter. This nucleus has descending projections to the spinal cord that can reduce pain input from the nociceptors. It also releases endogenous opioid compounds (endorphins and enkephalin) that act as hormones to reduce pain perception.

deep visceral pain often referred to superficial skin regions innervated by the same spinal cord segment; convergence may account for this phenomenon. Patterns of referred pain have obvious clinical diagnostic importance.

profound analgesia can result from electrical stimulation of some brain areas (areas produce endorphins and enkephalin) Substances are released as hormones into the blood--have widespread targets for blocking the reaction to pain; can also act directly as inhibitory neurotransmitters to block pain)

(act like morphine: this is the reason opiates have an effect--the brain has receptors sensitive to them

Release of compounds with morphine-like action

Physiological significance of endorphins and enkephalins.

(Important to sense trauma, not to be incapacitated by it, e.g., soldiers with wounds often not aware of injury until later, etc.)

This portion will present the structure and function of somatosensory receptors, with special emphasis on the low threshold mechanoreceptors of the skin.

Somatosensory receptors:

This spinal cord pathway is specialized for transmitting discriminative touch--sensations that are very precise in representing the intensity, location, submodality and timing of stimuli. We will study this pathway from skin receptors through processing in the cerebral cortex.

The Dorsal Column System:

This system is older phylogenetically, carries pain and temperature in addition to less precise touch and pressure sensations. We will again start at the periphery and carry the information transduced into the CNS and look at the processing of the information, especially pain.